Method of preparing buprenorphine

ABSTRACT

An improved process for preparing buprenorphine and a method for increasing the yield of buprenorphine or a derivative thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/349,213, filed Apr. 2, 2014, and claims priority benefit of PCTPatent Application No. PCT/GB2012/0542423, filed Oct. 1, 2012 and U.S.Provisional Patent Application No. 61/542,491, filed Oct. 3, 2011, thedisclosures of which are incorporated herein by reference in theirentireties for all purposes.

FIELD OF THE INVENTION

The present invention provides a process for the production of opiatealkaloids. In particular, the present invention provides an improvedprocess for the production of buprenorphine or a derivative ofbuprenorphine that increases overall yield and reduces impurities.

BACKGROUND OF THE INVENTION

Buprenorphine is a semisynthetic opiate used medicinally as a powerfulanalgesic, indicated for the treatment of moderate to severe pain andopioid dependence. The preparation of buprenorphine from thebaine isknown and has been reported in publications to be carried out by thefollowing 6 major step scheme:

The presently known method for preparing buprenorphine, however, hasseveral drawbacks. The method is an unspecific reaction scheme, that is,the method produces many other unwanted products, i.e., impurities,along with the buprenorphine. Thus, the buprenorphine has to be isolatedand purified, which is time consuming and inefficient.

Attempts have been made by others to improve the method of preparingbuprenorphine. For example, U.S. Patent No. 2010/0087647 to Allen, whichfocuses on step 3 of the known process, i.e., Grignard reaction. Thisimprovement retains the extraordinarily harsh conditions for removal ofthe methyl groups attached to the nitrogen and the phenolic oxygen andit therefore requires an additional purification step. Thus, therecontinues to be a need to improve the process of preparing buprenorphinethat improves the yield of buprenorphine, and limits or reduces thenumber of impurities formed during the process.

Definitions

Throughout this specification, the following abbreviations are used:cyanamide-norbuprenorphine-3-methyl ether (CMB); Norbuprenorphine3-Methyl Ether (NME); Norbuprenorphine crude (NOC); Norbuprenorphinepure (NOP).

The point of attachment of a moiety or substituent is represented by“—”. For example, —OH is attached through the oxygen atom.

“Alkyl” refers to a straight-chain, branched or cyclic saturatedhydrocarbon group. In certain embodiments, the alkyl group may have from1-20 carbon atoms, in certain embodiments from 1-15 carbon atoms, incertain embodiments, 1-8 carbon atoms. The alkyl group may beunsubstituted or substituted. Unless otherwise specified, the alkylgroup may be attached at any suitable carbon atom and, if substituted,may be substituted at any suitable atom. Typical alkyl groups includebut are not limited to methyl, ethyl, n-propyl, iso-propyl, cyclopropyl,n-butyl, iso-butyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl,cyclopentyl, n-hexyl, cyclohexyl and the like.

“Aryl” refers to an aromatic carbocyclic group. The aryl group may havea single ring or multiple condensed rings. In certain embodiments, thearyl group can have from 6-20 carbon atoms, in certain embodiments from6-15 carbon atoms, in certain embodiments, 6-12 carbon atoms. The arylgroup may be unsubstituted or substituted. Unless otherwise specified,the aryl group may be attached at any suitable carbon atom and, ifsubstituted, may be substituted at any suitable atom. Examples of arylgroups include, but are not limited to, phenyl, naphthyl, anthracenyland the like.

“Arylalkyl” refers to an optionally substituted group of the formulaaryl-alkyl-, where aryl and alkyl are as defined above.

“Halo” or “halogen” refers to —F, —Cl, —Br and —I.

“Morphinan” refers to a compound comprising the core structure:

“Substituted” refers to a group in which one or more (e.g. 1, 2, 3, 4 or5) hydrogen atoms are each independently replaced with substituentswhich may be the same or different. The substituent may be any groupwhich tolerates the demethylation reaction conditions. Examples ofsubstituents include but are not limited to —R^(a), —O—R^(a), —S—R^(a),—NR^(a)R^(b) and —NHR^(a); wherein R^(a) and R^(b) are independentlyselected from the groups consisting of alkyl, aryl and arylalkyl, andwherein R^(a) and R^(b) may be unsubstituted or further substituted asdefined herein.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an improvedmethod for the preparation of buprenorphine is provided that improvesthe overall yield of buprenorphine, and reduces the formation ofimpurities. Reduction of the formation of impurities is significant, asthe process heretofore known in the art is prone to produce a greatamount of impurities which requires purification and isolationprocesses.

Production of the impurities is believed to result in part fromdecomposition. It has been found by the present inventors thatsignificant formation of impurities, and large yield losses occur duringstep 5 of the prior art buprenorphine reaction scheme. Without beingheld to any theory, it is believed that the drastic conditions at stage5, i.e., demethylating the intermediate at 215° C., leads to both thedecomposition and discoloration of the intermediates of the process,thereby increasing impurity formation. In one embodiment of the presentinvention, the improved method of preparing buprenorphine includes twoseparate reaction steps after stage 4 of the process. It has been foundthat this modification to the prior art process for making buprenorphinecan occur at relatively mild conditions, and improves both overall yieldof the product and reduces impurities formation. In some embodiments, apurification step is optional and not necessary.

In one embodiment, the improved method for preparing buprenorphineincludes the following reaction steps shown below:

Reaction Scheme I

Referring to one exemplary reaction scheme as described and embodied inReaction Scheme I, the process includes steps 1 through 6. Step 1comprises contacting thebaine with a dienophile to form Formula II. Step2 comprises hydrogenating Formula II to form a compound comprisingFormula III. Step 3 comprises contacting the compound of Formula IIIwith t-BuMgX, wherein X is a halogen, to form the compound of FormulaIV. Step 4 comprises contacting Formula IV with XCN to form the compoundcomprising Formula V. Step 5A comprises charging the cyanamide (CMB)with a solvent and M¹OH to form Formula VI, i.e., Norbuprenorphine3-Methyl Ether (NME). Step 5B comprises charging a suitabledeprotonating base and a suitable base solvent, and RSH compound withFormula VI to form Formula VII, i.e., Norbuprenorphine crude (NOC). Step5C, an optional step, comprises purification of Formula VII, NOC, toform Norbuprenorphine pure (NOP). Step 6 includes contacting Formula VIIwith cyclopropylmethyl bromide to form buprenorphine base. In someembodiments, the yield of buprenorphine base is over about 50 to 80% ongoing from CMB to NOP. Purity was sufficiently improved by the processof the invention, such that step 5C, the purification step, is optional.It has been found that separating stage 5 into two separate stepsincreases the overall yield of the buprenorphine base. For example, butnot limitation, it has been found that conducting step 5 in three parts,5A, 5B, and 5C, with different reactants at milder conditions greatlyimproves overall yields and limits impurities.

DETAILED DESCRIPTION OF THE INVENTION Preparation of Buprenorphine

The present invention provides an efficient route for synthesizingbuprenorphine or its derivatives in high yield and high purity. Inparticular, processes have been discovered that efficiently and withfewer impurity-producing side-reactions convert thebaine or a derivativeof thebaine to buprenorphine or a derivative of buprenorphine. Inparticular, the overall yield of buprenorphine or a derivative ofbuprenorphine can be increased to greater than about 50 to 80% on goingfrom CMB to NOP.

In accordance with one embodiment of the invention, the method forpreparing buprenorphine or a derivative thereof includes the followingReaction Scheme I.

Wherein at steps 3 and 4, X is a halogen. The solvent is an alcohol,aqueous solution, or a combination thereof. For example and notlimitation, the alcohol can be a diol, such as diethylene glycol,ethylene glycol, or triethylene glycol. M¹ is a metal, including but notlimited to Na, K, Li. R is a C₁ to C₁₂ alkyl, branched or straightchain, a cycloalkyl-alkyl-, or an arylalkyl- and isomers thereof, and R¹is Me-, Et-, nPr-, iPr-, n-Bu-, secBu-, amyl-, and iamyl-. Further, atstep 5B, the RSH and R¹OM¹ preferably are in a solvent, such asdimethylformamide.

For example and not limitation, the improved process includes anexemplary embodiment as illustrated in Reaction Scheme II below.

Referring to Reaction Scheme II of the present embodiment step 5 isseparated into steps 5A, 5B, and 5C. In step 5A, the product of step 4is subjected to hydrolysis of the N-cyano group. In step 5B,norbuprenorphine 3-methyl ether, is subjected to hydrolysis of the3-O-Me group to produce crude norbuprenorphine. Finally, in step 5C, thecrude nor-buprenorphine is purified via its bitartrate salt to purenorbuprenorphine. The steps are further described below.

Step 5A: Preparation of Norbuprenorphine 3-Methyl Ether (NME)

In Step 5A, the N-cyano group is removed by hydrolysis. Step 5Acomprises contacting CMB with a hydrolysis agent (see Examples 1-3).

Typically, the hydrolysis agent is a compound having a pKa greater thanabout 12.0. Suitable compounds include group 1 and group 2 hydroxidesalts (such as, for example, KOH and Ca(OH)₂); and metal oxides (suchas, for example, lithium oxide, magnesium oxide, calcium oxide, and thelike). In a preferred embodiment the hydrolysis agent may be a hydroxideof a group 1 or group 2 metal. In an exemplary embodiment, thehydrolysis agent may be sodium hydroxide. The molar ratio between CMBand the hydrolysis agent can and will vary. Typically, the molar ratiomay vary from about 4 to about 8. In some exemplary embodiments, theratio was 1:6.

The hydrolysis agent may be added to the reaction mixture as a solutionof the hydrolysis agent in water. The concentration of the hydrolysisagent may range from about 10% to about 100%. In an exemplaryembodiment, the hydrolysis agent may be a 50% solution of sodiumhydroxide in water.

The CMB may be added to the reaction mixture either in solid form or asa solution in an appropriate organic solvent. In one exemplaryembodiment, CMB was added to the reaction mixture as a solution of CMBin dichloromethane. The solution was extracted from the reaction mixtureof the previous step in the overall scheme for preparation ofbuprenorphine.

The hydrolysis reaction mixture also includes an organic solvent. Avariety of organic solvents are suitable for use in the process of theinvention. Suitable organic solvents include, but are not limited to,ethylene glycol, diethylene glycol, triethylene glycol,2-methoxyethanol, 1-methoxy-2-propanol, and combinations thereof. Lowerboiling solvents such as methanol, ethanol, n-propanol, i-propanol arealso suitable. However, reaction times may be longer and excessive. Inan exemplary embodiment, the solvent may be diethylene glycol. Theweight ratio of the solvent to the CMB may vary. In general, the weightratio of the solvent to the CMB may range from about 2:1 to about 20:1.

In general, the hydrolysis reaction is conducted at a temperature thatranges from about 65° C. to about 125° C. In an exemplary embodiment,the reaction is conducted at about 116° C.

The reaction is preferably performed at ambient pressure, and preferablyin an inert atmosphere (such as, for example, nitrogen, helium, orargon).

In general, the pH of the reaction mixture will be at least about pH 14.In an exemplary embodiment, there is an excess of strong base frombeginning to the end, and the pH is always greater than 14. Depending onthe hydrolysis agent, the pH of the mixture may be adjusted with anappropriate pH-modifying agent to attain the desired pH value. Those ofskill in the art are familiar with suitable pH-modifying reagents.

Typically, the reaction is allowed to proceed for a sufficient period oftime until the reaction is complete. More specifically, the reactiongenerally is allowed to proceed until the level of NME no longerincreases. Those of skill in the art are familiar with suitabletechniques to measure the amount of NME in the reaction mixture. Onesuitable technique is liquid chromatography. Typically, the reaction isallowed to proceed for a period of time that ranges from about one hourto about 48 hours. In an exemplary embodiment, the reaction is allowedto proceed for 20 hours.

Upon completion of the reaction, water is added to the reaction mixtureand the reaction mixture is cooled. In an exemplary embodiment, thewater is added dropwise. The temperature of the reaction mixture isallowed to fall until within the range about 95° C. to about 105° C. Inan exemplary embodiment, the temperature is allowed to fall until withinthe range about 95° C. to about 100° C. The amount of water added to themixture may vary. Typically, the weight ratio of water to the CMB rangesfrom about 5:1 to about 50:1. In an exemplary embodiment, the weightratio of water to the CMB is 7.7:1.

After addition of the water, the reaction mixture is cooled over aperiod of time to cause precipitation of NME from the reaction mixture.The temperature of the reaction mixture is uniformly reduced until thetemperature is within the range about 0° C. to about 10° C. In anexemplary embodiment, the temperature is uniformly reduced until thetemperature is within the range 0° C. to 5° C. The period of time overwhich the reaction mixture is cooled may vary. Typically, the reactionmixture is cooled over a period of about 30 minutes to about threehours. In an exemplary embodiment, the reaction mixture is cooled over aperiod of two hours.

The precipitated NME may be easily separated from the reaction mixtureusing procedures well known to those of skill in the art.

Step 5B: Preparation of Crude Norbuprenorphine

In Step 5B, the 3-O-methyl group is removed to produce crudenorbuprenorphine (“NOC”). Step 5B comprises contacting NME with anO-demethylation agent (see Examples 4-6). The O-demethylation agent canbe, for example, a combination of a mercaptan and a strong organic base.Suitable mercaptans include mercaptans of alkanes, carboxylic acids. Inan exemplary embodiment the O-demethylation agent may ben-propylmercaptan. The molar ratio between NME and the O-demethylationagent can and will vary. Typically, the molar ratio may vary from about1:5 to about 1:1. In some exemplary embodiments, the ratio was about1:2.

Suitable organic bases include lithium, sodium, and potassium salts ofalcohols. In an exemplary embodiment the organic base was Sodiumtert-butoxide.

The O-demethylation reaction includes an organic solvent. A variety oforganic solvents are suitable for use in the process of the invention.Suitable organic solvents include, but are not limited to,dimethylformamide, dimethylacetamide, N-methylpyrrolidinone, DMSO,sulfolane, other dialkylamide solvents, and combinations, thereof. In anexemplary embodiment, the solvent was dimethylformamide. The weightratio of the solvent to the NME may vary. In general, the weight ratioof the solvent to the NME may range from about 2:1 to about 20:1. In anexemplary embodiment, the weight ratio of the solvent to the NME wasabout 13:1.

The NME, the mercaptan, and the organic base may be added to thereaction mixture. In one particular embodiment, the NME is added last.In an exemplary embodiment, sodium tert-butoxide was added first,followed by the 1-propanethiol, followed by NME.

The reaction is preferably performed at ambient pressure, and preferablyin an inert atmosphere (such as, for example, nitrogen, helium, orargon). In an exemplary embodiment, the reaction vessel was evacuated to60 torr and filled with nitrogen three times before charging reactants.

In general, the O-demethylation reaction is conducted at a temperaturethat ranges from about 100° C. to about 125° C. In an exemplaryembodiment, the reaction is conducted at a temperature between 115 and125° C.

In general, the pH of the reaction mixture will be at least about pH 14.In this regard, the molar amount of base exceeds the molar amount ofmercaptan.

Typically, the reaction is allowed to proceed for a sufficient period oftime until the reaction is complete. More specifically, the reactiongenerally is allowed to proceed until the level of NOC no longerincreases. Those of skill in the art are familiar with suitabletechniques to measure the amount of NOC in the reaction mixture. Onesuitable technique is liquid chromatography. Typically, the reaction isallowed to proceed for a period of time that ranges from about one hourto about 48 hours. In an exemplary embodiment, the reaction is allowedto proceed for 12 hours.

Upon completion of the reaction, the reaction mixture is cooled. Thetemperature of the reaction mixture is allowed to fall until within therange about 60-100° C. In an exemplary embodiment, the temperature isallowed to fall until about 80° C.

After this cooling step, the reaction mixture is quenched by reducingthe pH of the reaction mixture. For example but not limitation, sodiumbicarbonate can be added to reduce the pH to approximately 7 or 9, sothat strong base will not be an impurity in the precipitated product.The pH lowering agent may be dissolved in water. Examples of suitable pHlowering agents include sodium bicarbonate, mineral acid, e.g., dilutehydrochloric or sulfuric, or organic acid, e.g., acetic acid,preferably, the pH reducing agent is sodium bicarbonate. In an exemplaryembodiment, the pH lowering agent was sodium bicarbonate dissolved inwater.

The pH precipitation occurs over a period of time. The period of timeover which the pH precipitation occurs may vary. Typically, the pHprecipitation occurs over a period of 15 minutes to two hours. In anexemplary embodiment, the pH precipitation occurred over a course of onehour.

After the pH precipitation, the reaction mixture is cooled over a periodof time to further encourage precipitation of NOC from the reactionmixture. The temperature of the reaction mixture is uniformly reduceduntil the temperature is within the range about 0° C. to about 10° C. Inan exemplary embodiment, the temperature is uniformly reduced until thetemperature is within the range 0° C. to 5° C. The period of time overwhich the reaction mixture is cooled may vary. Typically, the reactionmixture is cooled over a period of about 30 minutes to about threehours. In an exemplary embodiment, the reaction mixture is cooled over aperiod of two hours.

The precipitated NOC may be easily separated from the reaction mixtureusing procedures well known to those of skill in the art.

The NOC thus produced may be used without purification in the sixth andfinal step of the buprenorphine process described above, or it may befurther purified before such use.

Step 5C: Purification of Crude Norbuprenorphine to Pure Norbuprenorphine

In step 5C, the crude norbuprenorphine is purified to produce purenorbuprenorphine (NOP). The crude norbuprenorphine is purified byconverting it to an organic acid salt, followed by production of thepurified free-base norbuprenorphine.

The organic acid salt is produced by contacting the NOC with an organicacid. Typically, the organic acid used to form the salt is a carboxylicacid or a di-carboxylic acid. Suitable acids include tartaric acid. Inan exemplary embodiment the organic acid was L-tartaric acid. In anexemplary embodiment, the ratio was about 1:1.

The salt formation reaction includes an organic solvent. A variety oforganic solvents are suitable for use in the process of the invention.Suitable organic solvents include, but are not limited to, polarsolvents, small alcohols and acetone, and combinations, thereof. In anexemplary embodiment, the solvent was isopropyl alcohol. The weightratio of the solvent to the NOC may vary. In general, the weight ratioof the solvent to the NME may range from about 5:1 to about 30:1. In anexemplary embodiment, the weight ratio of the solvent to the NME wasabout 20:1.

In general, the salt formation reaction is conducted at a temperaturethat ranges from about 60° C. to 80° C. In an exemplary embodiment, thereaction was conducted at a temperature between 70° C. and 75° C.

Typically, the reaction is allowed to proceed for a sufficient period oftime until the reaction is complete. More specifically, the reactiongenerally is allowed to proceed until cloudiness is seen and crystalformation has begun. If cloudiness is not observed, those of skill inthe art are familiar with techniques for seeding crystallization of thereaction system. In an exemplary embodiment, a small amount of thesolution was withdrawn and scratched to created seed crystals, thenreturned to the flask.

Upon completion of the reaction, the reaction mixture is cooled over aperiod of time to further encourage precipitation of the salt from thereaction mixture. The temperature of the reaction mixture is allowed tofall until within the range about 40-55° C. In an exemplary embodiment,the temperature is allowed to fall until between 50° C. and 80° C. Theperiod of time over which the reaction mixture is cooled may vary.Typically, the reaction mixture is cooled over a period of about 30minutes to about three hours. In an exemplary embodiment, the reactionmixture is cooled over a period of two hours.

The precipitated salt may be easily separated from the reaction mixtureusing procedures well known to those of skill in the art.

The salt is converted to NOP by contacting the salt with an inorganicbase. Typically, the inorganic base is a hydroxide of a group 1 or group2 metal. In an exemplary embodiment, the inorganic base may be sodiumhydroxide.

The base regeneration from the salt reaction uses water as a solvent.The weight ratio of the solvent to the salt may vary. In general, theweight ratio of the solvent to the salt may range from about 20:1 toabout 100:1. In an exemplary embodiment, the weight ratio of the solventto the salt was about 47:1.

In general, the base regeneration from the salt reaction is conducted ata temperature that ranges from about 40° C. to about 80° C. Thetemperature may vary within this range during the course of thereaction. In an exemplary embodiment, the reaction was conducted at atemperature between 45° C. and 55° C. in an initial portion of thereaction, and between 65° C. and 75° C. in a later portion of thereaction.

To produce the desired NOP, the inorganic base is added to a solution ofthe salt to adjust the pH to a value above 9.0. In an exemplaryembodiment, the pH was maintained within the range 9.0 to 9.5. This pHadjustment causes precipitation.

The reaction is allowed to proceed at the designated pH for a sufficientperiod of time until material forms a more readily filterableprecipitate. More specifically, the reaction generally is allowed toproceed until the solution becomes thick with precipitate, then thinsout. In an exemplary embodiment, this process took twenty minutes.

Upon completion of the reaction, the reaction mixture is filteredwithout cooling. The resulting filtrate may be washed with water anddried using procedures well known to those of skill in the art.

In one embodiment, an improved process for preparing buprenorphine isprovided, wherein the steps include contacting thebaine with adienophile to form Formula II, hydrogenating Formula II to form acompound comprising Formula III, contacting the compound of Formula IVwith XCN to form the compound of Formula V, the improvement comprisingsubjecting the compound of Formula V to hydrolysis, e.g., of the N-cyanogroup, and further subjecting the product of the first hydrolysis to asecond hydrolysis, e.g., the 3-O-Me group. In this regard, the productof the two hydrolysis steps produces norbuprenorphine. Thenorburprenorphine is contacted with an agent to form buprenorphine base.In some embodiments, the nor-burprenorphine is purified.

3-O-demethylation of Morphinans

In another aspect, the present invention provides a process for thepreparation of a compound of formula (Ib),

wherein:

R₁₀ is a straight-chain, branched or cyclic C₁-C₂₀ alkyl;

R₁₁ is —C(R₁₃)(R₁₄)(OH) or a protected —C(═O)(R₁₅);

R₁₂ is H or CN;

R₁₃ is a straight-chain, branched or cyclic C₁-C₂₀-alkyl;

R₁₄ is a straight-chain, branched or cyclic C₁-C₂₀-alkyl;

R₁₅ is a straight-chain, branched or cyclic C₁-C₂₀-alkyl and

is a double bond or a single bond;

the process comprising:

-   -   i. reacting a compound of formula (Ia) with a thiolate in a        suitable polar aprotic solvent, wherein the thiolate is selected        from the group consisting of an optionally substituted        C₁-C₂₀-alkylthiolate, an optionally substituted        C₆-C₂₀-arylthiolate or an optionally substituted        C₇-C₃₀-arylalkylthiolate; and        -   ii. treating the reaction mixture of step (i) with a            protonating agent to give the compound of formula (Ib).

R₁₀ is a straight-chain, branched or cyclic C₁-C₂₀ alkyl, preferably astraight-chain C₁-C₂₀ alkyl. In one embodiment, R₁₀ is a C₁-C₁₅ alkylgroup, such as a C₁-C₁₀ alkyl, for example, a C₁-C₅ alkyl. In onepreferred embodiment, R₁₀ is -Me.

R₁₁ is —C(R₁₃)(R₁₄)(OH), wherein R₁₃ and R₁₄ are independentlystraight-chain, branched or cyclic C₁-C₂₀-alkyl groups. In oneembodiment, R₁₁ is

In another embodiment, R₁₁ is

In yet another embodiment, R₁₁ is

R₁₁ can be a protected —C(═O)(R₁₅). In one embodiment, the keto groupmay be protected as an acetal or a ketal as described below. In onepreferred embodiment, R₁₅ is -Me. In one embodiment, the protectinggroup may be removed by methods known in the art to form —C(═O)(R₁₅).

Interestingly, the present inventors have found that when the aminogroup of compound (Ia) is substituted with an -alkylcycloalkyl groupsuch as -methyl-cyclopropane, the 3-O-demethylation reaction does notappear to work efficiently.

The O-demethylation step may affect other substituents of the morphinansusceptible to basic conditions or reactive towards nucleophiles, suchas keto groups. Thus, it is may be desirable to first protect the ketogroup with a suitable protecting group which may be optionally removedafter the O-demethylation step is completed. Protecting groups are knownin the art and methods for their introduction and removal are describedin standard references such as “Greene's Protective Groups in OrganicSynthesis”, P. G. M. Wuts and T. W. Greene, 4th Edition, Wiley. Suitableketo protecting groups include but are not limited to acetals andketals. For example, substituted or unsubstituted, straight-chain orbranched C₁-C₂₀-alkanols, substituted or unsubstituted, straight-chainor branched 1,2-(C₁-C₂₀)-alkyl-diols (for example, ethylene glycol or1,2-propanediol), or substituted or unsubstituted, straight-chain orbranched 1,3-(C₁-C₂₀)-alkyldiols may be conveniently utilized to formsuitable acetals or ketals. A diol reacts to form a ring and in thisinstance, the ketal comprises substituted or unsubstituted chiral orachiral bridges which are derived, for example, from the skeletons—(CH₂)_(n)— (n=2, 3 or 4), —CH(CH₃)CH(CH₃)—, —CH(CH₃)CH₂CH(CH₃)—,—CMe₂-, —CHMe-, no limitation being implied by this listing.

The process of the present invention can be performed on morphinanscomprising unprotected hydroxyl groups. However, if desired, the hydroxygroups may be first protected with a protecting group which may beoptionally removed after the O-demethylation step is completed. Suitableprotecting groups include but are not limited to alkyl, aryl (e.g.phenyl), benzyl, acyl and silyl groups. Other suitable protecting groupsare described in Wuts and Greene above.

The thiolate does not appear to react with unconjugated —C═C— doublebonds. Accordingly, the process of the present invention may be carriedout on morphinans comprising this functional group. In one embodiment,therefore,

is a —C═C— double bond. Alternatively,

can be a —C—C— single bond.

The thiolate is selected from the group consisting of an optionallysubstituted C₁-C₂₀-alkylthiolate, an optionally substitutedC₆-C₂₀-arylthiolate or an optionally substitutedC₇-C₃₀-arylalkylthiolate. In one preferred embodiment, the thiolate isunsubstituted.

In one embodiment, the thiolate is substituted. An example of asubstituted alkylthiolate is MeO₂C—CH₂CH₂S⁻.

In one embodiment, the alkyl group of the alkylthiolate comprises 2 to 4carbon atoms, for example, propanethiolate. In another embodiment, thealkyl group of the alkylthiolate comprises greater than 4 carbon atoms,such as 5 or more carbons, for example, 8 or more carbons. In onepreferred embodiment, the alkylthiolate is a C₁₀-C₂₀-alkylthiolate. Inone particularly preferred embodiment, the alkylthiolate is adodecanethiolate salt. Unlike other thiolates, the use ofdodecanethiolate is advantageous as it is significantly less odorousthan other thiolates.

An example of a suitable C₆-C₂₀-arylthiolate includes but is not limitedto phenylthiolate. An example of a suitable C₇-C₃₀-arylalkylthiolateincludes but is not limited to phenylmethylthiolate.

In some embodiments, the thiolate may be an alkylthiolate, arylthiolateor arylalkylthiolate tethered to an insoluble support. In oneembodiment, the insoluble support is a suitable organic support (such aspolystyrene). In another embodiment, the insoluble support is a suitableinorganic support.

The counter cation of the thiolate is typically an alkali metal cationi.e. Li⁺, Na⁺ or K⁺.

The thiolate may be a commercially available thiolate salt.Alternatively, the thiolate may be prepared from a thiol and a basewhich is capable of deprotonating the thiol. Suitable bases aregenerally those where the pKa of the conjugate acid is greater thanabout four units higher than the pKa of the thiol. In this regard, theapproximate pKa of a typical alkylthiol is about 10. Consequently,deprotonation of the alkylthiol may be achieved with the use of a basewhere the pKa of the conjugate acid is greater than about 14. Examplesof suitable bases include but are not limited to alkali metal alkoxides(e.g. sodium or potassium methoxide, sodium or potassium ethoxide,sodium or potassium propoxide or sodium or potassium butoxide), alkalimetal hydroxides (such as sodium or potassium hydroxide), alkali metalhydrides (e.g. sodium hydride), organolithium reagents (such asbutyllithium) or alkali metal amides (e.g. NaNH₂ or KNH₂).

The molar ratio between the compound (Ia) and the thiolate can and willvary. Typically, the molar ratio will vary from about 1:5 to about 1:1.In some exemplary embodiments, the ratio may be about 1:3, and inothers, about 1:1.5.

The compound of formula (Ia) is reacted with the thiolate in a suitablepolar aprotic solvent. By “polar aprotic solvent” we mean a liquidmedium with a high dielectric constant and dipole moment which does nothave an acidic hydrogen. The high polarity of the solvent allows it todissolve charged species such as nucleophiles (i.e. the thiolate) butthe absence of an acidic hydrogen increases the reactivity ofnucleophiles as they are less solvated in solution. The polar aproticsolvent is also able to dissolve the compound of formula (Ia) to formsolutions which are preferably in the range of about 0.01-2 mol/L,preferably about 0.05-1.0 mol/L, more preferably about 0.1-0.8 mol/L.While a small quantity of water may be present in the O-demethylationreaction mixture (i.e. <0.55% w/w water), the solvent is preferablyanhydrous. Suitable polar aprotic solvents preferably have boilingpoints at atmospheric pressure (i.e. 1.0135×10⁵ Pa) above 140° C. andmore preferably above 150° C. Such solvents generally allow the reactionto be carried out at the optimum temperature to minimize reaction timeand impurity generation. Preferred examples are dialkylamide solvents(e.g. dimethylformamide or dimethylacetamide), or cycloalkylamidesolvents (e.g. N-methyl-2-pyrrolidone) or combinations thereof. Otherexamples include dimethylsulfoxide, sulfolane, hexamethylphosphoramideor combinations thereof.

The reaction of step (i) is preferably performed at ambient pressure,and preferably in an inert atmosphere (such as, for example, nitrogen,helium or argon).

In general, the reaction of step (i) may be conducted at a temperaturein the range of about 100° C. to about 130° C. In an exemplaryembodiment, the reaction is conducted at a temperature between about115° C. and about 125° C.

Typically the reaction of step (i) is allowed to proceed for asufficient period of time until the reaction is complete. Morespecifically, the reaction generally is allowed to proceed until thelevel of compound of formula (Ib) no longer increases. Those of skill inthe art are familiar with suitable techniques to measure the amount ofcompound (Ib) in the reaction mixture. One suitable technique is HPLC.Typically, the reaction is allowed to proceed for a period of time thatranges from about one hour to about 48 hours. In an exemplaryembodiment, the reaction is allowed to proceed for 12 hours or less. Incertain embodiments, the reaction is allowed to proceed for 6 hours orless.

A variety of conditions may be selected in order to help minimize oreliminate the production of impurities by over demethylation at C-6.These conditions include the temperature at which step (i) is conductedand/or the time for which the reaction is allowed to proceed.

In step (ii) the reaction mixture of step (i) is treated with aprotonating agent to give the compound of formula (Ib). Without wishingto be bound by theory, it is believed that the protonating agentquenches the 3-O-phenolate anion to provide the compound (Ib). Suitableprotonating agents include aqueous solutions of an alkali metalbicarbonate (e.g. sodium or potassium bicarbonate). Without wishing tobe bound by theory, it is believed that the bicarbonate decomposes toform a carbonate and protons.

The reactants may be added in any suitable order. In one preferredprocess of the invention, the compound (Ia) with a solvent (if used) isadded to a reaction mixture of the thiolate in solvent and is reactedfor a time and under conditions sufficient for compound (Ia) to beO-demethylated, followed by the addition of the protonating agent inorder to form the compound (Ib).

Upon completion of the reaction, the reaction mixture may be treated asgenerally described above in connection with Step 5B, i.e. thepreparation of crude norbuprenorphine.

Various compounds of formula (Ia) may be treated according to theprocesses described herein to yield compounds of formula (Ib) asillustrated below:

In another aspect, the present invention provides a process for thepreparation of a compound of formula (IIb),

wherein:

-   -   R₂₀ and R₂₁ are independently selected from substituted or        unsubstituted C₁-C₂₀ alkyl or R₂₀ and R₂₁ are interconnected to        form a ring;    -   R₂₂ is H or OH;    -   R₂₃ is selected from the group consisting of H, CN, substituted        C₁-C₂₀ alkyl, unsubstituted C₁-C₂₀ alkyl, substituted        C₄-C₂₀-alkyl-cycloalkyl, unsubstituted C₄-C₂₀-alkyl-cycloalkyl        and allyl;    -   is a double bond or a single bond;    -   the process comprising:        -   i. reacting a compound of formula (IIa) with a thiolate in a            suitable polar aprotic solvent, wherein the thiolate is            selected from the group consisting of an optionally            substituted C₁-C₂₀-alkylthiolate, an optionally substituted            C₆-C₂₀-arylthiolate or an optionally substituted            C₇-C₃₀-arylalkylthiolate; and        -   ii. treating the reaction mixture of step (i) with a            protonating agent to give the compound of formula (IIb).

When R₂₀ and R₂₁ are interconnected to form a ring, the two groups mayform a ketal as generally described above. In one embodiment, the groupsmay form substituted or unsubstituted chiral or achiral bridges whichare derived, for example, from the skeletons —(CH₂)_(n)— (n=2, 3 or 4),—CH(CH₃)CH(CH₃)—, —CH(CH₃)CH₂CH(CH₃)—, —CMe₂-, —CHMe-, no limitationbeing implied by this listing.

In one embodiment, R₂₂ is H. In another embodiment, R₂₂ is OH.

In one embodiment, R₂₃ may be H, in another embodiment CN, and in yetanother embodiment allyl (i.e. —CH₂CH═CH₂). When R₂₃ is an unsubstitutedC₁-C₂₀ alkyl, R₂₃ is preferably -Me. When R₂₃ is an unsubstitutedC₄-C₂₀-alkyl-cycloalkyl, R₂₃ is preferably cyclopropylmethyl-

or cyclobutylmethyl-

In one embodiment,

is a —C═C— double bond. In another embodiment,

is a —C—C— single bond.

The compound (IIb) may be deprotected to form a keto group at C-6. Inone embodiment, therefore, the process further comprises converting thecompound of formula (IIb) to a compound of formula (IIc):

The compound (IIb) may be isolated and optionally purified before beingdeprotected. In this instance, the deprotection may be performed bymethods known in the art. Alternatively, the 3-O-demethylationconditions of step (i) and/or (ii) may adapted such that thedeprotection step also occurs in a one-pot reaction.

In another aspect, the present invention provides a process for thepreparation of a compound of formula (IIIb),

wherein:

R₃₀ is an alcohol protecting group;

R₃₁ is H or OH; and

R₃₂ is selected from the group consisting of H, CN, substituted C₁-C₂₀alkyl, unsubstituted C₁-C₂₀ alkyl, substituted C₄-C₂₀-alkyl-cycloalkyl,unsubstituted C₄-C₂₀-alkyl-cycloalkyl and allyl;

the process comprising:

-   -   i. reacting a compound of formula (IIIa) with a thiolate in a        suitable polar aprotic solvent, wherein the thiolate is selected        from the group consisting of an optionally substituted        C₁-C₂₀-alkylthiolate, an optionally substituted        C₆-C₂₀-arylthiolate or an optionally substituted        C₇-C₃₀-arylalkylthiolate; and    -   ii. treating the reaction mixture of step (i) with a protonating        agent to give the compound of formula (IIIb).

R₃₀ is an alcohol protecting group. In one embodiment, R₃₀ is selectedfrom substituted or unsubstituted C₁-C₂₀ alkyl. Alternatively, R₃₀ maybe a silyl protecting group such as a substituted or unsubstituted(C₁-C₂₀-alkyl)₃Si— (such as Me₃Si— (TMS), ^(t)BuMe₂Si— (TBDMS) or^(i)Pr₃Si— (TIPS)), a substituted or unsubstituted(C₁-C₂₀-alkyl)(C₆-C₂₀-aryl)₂Si— (for example, ^(t)BuPh₂Si— (TBDPS)) or asubstituted or unsubstituted (C₁-C₂₀-alkyl)₂(C₆-C₂₀-aryl)Si—.

In one embodiment, R₃₁ is H. In another embodiment, R₃₁ is OH.

In one embodiment, R₃₂ may be H, in another embodiment CN, and in yetanother embodiment allyl (i.e. —CH₂CH═CH₂). When R₃₂ is an unsubstitutedC₁-C₂₀ alkyl, R₃₂ is preferably -Me. When R₃₂ is an unsubstitutedC₄-C₂₀-alkyl-cycloalkyl, R₃₂ is preferably cyclopropylmethyl-

or cyclobutylmethyl-

The compound (IIIb) may be deprotected to form a keto group at C-6. Inone embodiment, therefore, the process further comprises converting thecompound of formula (IIIb) to a compound of formula (IIIc):

The compound (IIIb) may be isolated and optionally purified before beingdeprotected. In this instance, the deprotection may be performed bymethods known in the art. Alternatively, the 3-O-demethylationconditions of step (i) and/or (ii) may adapted such that thedeprotection step also occurs in a one-pot reaction.

The reaction conditions for steps (i) and (ii) in the preparation ofcompounds (IIb) or (IIIb) are as generally described above for thepreparation of compound (Ib).

Impurities which may be specified in the Official Monographs formorphinans such as oxymorphone include α,β-unsaturated ketones (ABUKs),such as 14-hydroxymorphinone. There has been much recent concern overABUKs due to their proposed biological activities as carcinogens. Assuch, there is a continuing need to develop processes which produce lowABUK morphinans, in particular low ABUK oxymorphone alkaloid orhydrochloride. Low ABUK oxymorphone may be prepared using the processesof the present invention starting from low ABUK oxycodone. For example,low ABUK oxycodone may be protected to form compounds (IIa) or (IIIa).Low ABUK oxymorphone therefore may be prepared via compounds (IIb) or(IIIb).

Thus, in one embodiment, the oxymorphone alkaloid prepared according tothe present invention comprises ≤about 25 ppm of an α,β-unsaturatedketone, such as ≤about 20 ppm of an α,β-unsaturated ketone, for example,≤about 15 ppm of an α,β-unsaturated ketone. In one preferred embodiment,the oxymorphone alkaloid comprises ≤about 10 ppm of an α,β-unsaturatedketone. In another embodiment, the oxymorphone alkaloid is substantiallyfree of an α,β-unsaturated ketone.

EXAMPLES

The following examples are included to demonstrate exemplary embodimentsof the invention. It should be appreciated by those of skill in the artthat the techniques disclosed in the following examples representtechniques discovered by the inventors to function well in the practiceof the invention. Those of skill in the art should, however, in light ofthe present disclosure, appreciate that many changes could be made inthe specific embodiments that are disclosed and still obtain a like orsimilar result without departing from the spirit and scope of theinvention, therefore all matter set forth is to be interpreted asillustrative and not in a limiting sense.

Example 1: CMB Decyanation

45.26 g CMB (100 mmol) was added to 400 mL ethylene glycol and 48 g of50% NaOH/H₂O (600 mmol), stirred under nitrogen, and slowly heated to120° C. The reaction mixture was maintained at 115-125° C. forapproximately 12 hours, after which it was allowed to cool to roomtemperature. The mixture was re-heated to 120° C. and 400 mL water wasadded dropwise over the course of approximately 40 minutes, during whichtime the temperature was reduced to 100-105° C. The mixture was cooledto 4° C. over approximately 1.5 hours. The resulting precipitate wasfiltered, washed with water, and dried in a 60° C. vacuum oven. Theresult was 40.99 g NME (95.9% yield), and its liquidchromatography-measured purity at 210 nm was 96.04%.

Example 2: CMB Decyanation

9.05 g CMB (20 mmol) was added to 100 mL ethylene glycol and 9.6 g of50% NaOH/H₂O (120 mmol), stirred under nitrogen, and maintained at 130°C. After approximately 55 minutes, some water was allowed to evaporate,and an odor of ammonia was detected in the escaping gas. After anotherapproximately one hour and ten minutes, the reaction mixture was allowedto cool to room temperature. The resulting precipitate was washed withwater and dried in a vacuum oven at 60° C. The resulting product was7.99 g (93.5% yield), and its liquid chromatography-measured purity at210 nm was 96.22%.

Example 3: CMB Decyanation

45.26 g CMB (100 mmol) was added to 350 mL 2-methoxyethanol and 48 g of50% NaOH/H₂O (600 mmol), stirred under nitrogen, and maintained atapproximately 110-120° C. After approximately 20 hours, 100 mL of waterwas added, and the temperature to drop to 93.5° C. The mixture was keptat 95-100° C. and 250 mL more of water was added for a total of 350 mLwater. The reaction mixture was cooled to 3° C. over 1.5 hours. Theresulting precipitate was filtered, washed with water, and dried at 60°C. in a vacuum oven for 3 hours. The resulting product was 40.56 g(94.9% yield), and its liquid chromatography-measured purity at 210 nmwas 97.77%.

Example 4: NME O-demethylation with nPrSNa

2.14 g NME (5 mmol), 0.98 g sodium n-propylmercaptide (10 mmol), and 35mL DMF were stirred under nitrogen. The reaction mixture was heated to120° C. and refluxed for 12 hours and allowed to cool to roomtemperature. 14 mL of 6% NaHCO₃ (10 mmol) was added, then 56 mL water.The mixture was cooled to 2° C. The resulting precipitate was filtered,washed well with water, and dried to produce 1.58 g NOC (76% yield), andits liquid chromatography-measured purity at 210 nm was 92.10%.

Example 5: NME O-demethylation with PrSH/NaOt-Bu

21.38 g NME (50 mmol) and 9.61 g NaOt-Bu (100 mmol) were dissolved in350 mL DMF. 9.5 mL 1-propanethiol (105 mmol) were added, producing apurple solution. The reaction mixture was stirred under Nitrogen, heatedto 120° C. over approximately one hour, refluxed at 115-125° C. forapproximately 12 hours, then allowed to cool to room temperature. Asolution of 8.4 g NaHCO₃ in 700 mL water was added and the mixture wascooled to 0-5° C. The resulting precipitate was filtered and washedtwice with cold water. The filter cake was dried, producing 14.59 g NOC(70.6% yield), and its liquid chromatography-measured purity at 210 nmwas 92.59%.

Example 6: NME O-demethylation with PrSH/NaOt-Bu

A reaction vessel was carefully purged of nitrogen, with three 60 Torrvacuum-Nitrogen purges. The reaction vessel was thereafter carefullypreserved from exposure to the atmosphere. 6.82 g sodium tert-butoxide(71.0 mmol) was dissolved in 45 mL DMF with stirring, producing a purplesolution. 6.7 mL 1-propanethiol (74.3 mmol) were added via syringe. Tothis mixture was added a solution of 14.45 g NME (33.79 mmol) in 120 mLwarm DMF, followed by a 12 mL DMF rinse. The reaction mixture was heatedto 120° C. and refluxed at 115-125° C. for approximately 12 hours, thenallowed to cool to room temperature. The mixture was then heated to 80°C. and a solution of 5.96 g NaHCO₃ in 354 mL water was added dropwiseover one hour as the temperature was maintained at 75-85° C. The mixturewas then cooled to 0-5° C. over two hours. The resulting precipitate wasfiltered and twice washed with 100 mL cold water. Upon vacuum drying at80° C., 11.85 g of NOC was obtained (85.8% yield), and its liquidchromatography-measured purity at 210 nm was 95.00%.

Example 7: Preparation of Pure Nor-Buprenorphine

10.21 g crude norbuprenorphine base (24.69 mmol) and 3.78 gramsL(+)-tartaric acid (25.18 mmol) were dissolved in 219 ml IPA and broughtto 70 to 75° C. A small amount of the solution was withdrawn andscratched for seed crystal, then returned to the flask. When cloudinesswas seen and crystal formation had begun, the mixture was cooled to 50to 55° C. over a two hour period, then held in that temperature rangefor one hour longer. The slurry was filtered and the wet cake was washedwith 30 ml IPA, then dried in a 60° C. vacuum oven. The bitartrate saltweighed 12.40 grams (89.1% yield).

10.89 g of the above bitartrate salt (19.32 mmol) was added to 511 ml ofwater and brought to 45 to 55° C. The pH was adjusted to 9.0 to 9.5 bythe addition of 2M sodium hydroxide solution. The temperature wasincreased to 65 to 75° C. The solution became thick with precipitate butthinned out after 20 minutes of stirring. A few drops of 2M NaOH wereadded to return the pH, which had fallen to 8.97, back into the range9.0 to 9.5. The solution was filtered hot and washed with approximately50 ml of water. The wet cake was dried in an 80° C. vacuum oven to give7.64 grams of pure norbuprenorphine base (96.7% recovery). Overall yieldfor this step was 86.2%.

Example 8: Preparation of NME

44.16 g N,O-Dimethylnorbuprenorphine (100 mmol), 6.22 g freshly powderedpotassium carbonate (45 mmol), and 13.66 g cyanogen bromide were addedto 101 mL dichloromethane. The slurry was placed under nitrogen andstirred and heated to reflux for ten hours, then stirred without heatfor 12 hours. The mixture was cooled to 0-5° C., then 7.4 mLconcentrated ammonium hydroxide was added. The solution was stirred fortwo hours at 0-10° C., then 54 mL of water was added and the mixture wasstirred for ten minutes longer, then left to rest for at least 30minutes. The layers were separated. The upper aqueous layer wasextracted with 17 mL dichloromethane. The combined organic layers wereextracted with a solution prepared from 1.3 mL concentrated ammoniumhydroxide, 49 mL water, and 10 mL 20% aqueous sodium chloride. Theorganic layer was then extracted twice more, each time with a solutionprepared from 49 mL water and 10 mL 20% aqueous sodium chloride. Theyellow organic layer containing CMB weight 192.0 grams.

192.0 grams of the above CMB solution was added to 226 mL diethyleneglycol and placed under nitrogen. The solution was slowly warmed to atemperature of 120° C. while dichloromethane distilled out. The solutionwas held at 120° C. for 30 minutes longer, then cooled to 85° C. 48 gsodium hydroxide solution (50%, 600 mmol) was then added slowly,allowing the temperature to rise to 100° C. The temperature was broughtto 115 to 125° C. and held for ten hours, then cooled to 100° C. 453 mLwater was then added dropwise while maintaining the temperature at90-100° C. The solution was then cooled over a three-hour period to 0-5°C. The slurry was filtered and the NME product was dried in a 60° C.vacuum oven. The yield was 40.32 g (93% yield fromN,O-dimethylnorbuprenorphine), approximately 98% pure.

Example 9: NME O-demethylation with 1-propanethiol/NaO^(t)Bu

A flange flask was set up and purged with nitrogen. Sodium tert-butoxide(4.7 g, 0.05 moles) and dimethylformamide (DMF) (31.0 mL, 0.4 moles)were charged to the flask and stirred for 5 minutes. No change in colourwas observed. 1-Propanethiol (5.0 mL, 0.06 moles) was charged. A whiteprecipitate was produced and a slight exotherm was observed. The mixturewas stirred for 20 minutes.

Meanwhile, a solution of NME (10.0 g, 0.02 moles) in DMF (83.0 mL, 1.07moles) was prepared. The solution was gently heated to dissolve thesolid. After 20 minutes, the NME solution was charged to the sodiumpropanthiolate solution followed by a DMF rinse (8.0 mL, 0.1 moles).Whilst stirring, the temperature was increased to 115-125° C. over aperiod of 30 minutes and held at this temperature range with stirringfor 20 hours.

After 20 hours, the reaction mixture was cooled to 80° C. and a solutionof sodium bicarbonate (4.1 g, 0.05 moles) in water (245 mL, 13.6 moles)was added dropwise over a period of 2 hours. The mixture was then cooledto 0-5° C. and the resulting precipitate filtered, washed with water(2×200 mL) and dried overnight to produce 7.29 g of norbuprenorphine(75.1% yield) having a purity of 94.03% by area as determined by HPLC(λ=288 nm).

Example 10: NME O-demethylation with 1-dodecanethiol/KO^(t)Bu

Potassium tert-butoxide (5.9 g, 0.05 moles) was charged to a flangeflask and the flask purged with nitrogen. DMF (105.0 mL, 1.36 moles) wascharged and the mixture stirred until the solid had dissolved.1-Dodecanethiol (12.6 mL, 0.05 moles) was added and a white precipitatewas formed. NME (15.0 g, 0.035 moles) was charged and washed in with DMF(15.0 mL, 0.19 moles). The mixture was heated to 115-125° C. The mixturewas cooled to 90° C. after 2.25 hours heating. A solution of sodiumbicarbonate (6.18 g, 0.07 moles) in water (240 mL, 13.3 moles) was addeddropwise to the mixture whilst maintaining the temperature at 85-95° C.The mixture was then cooled to <5° C., filtered, washed with water(2×200 mL), dried, treated with heptane and dried to produce 12.383 g ofnorbuprenorphine (85.3% yield) having a purity of 93.8% by area asdetermined by HPLC (λ=288 nm).

Example 11: Alternative O-demethylating Reagents

Based on the procedure of Example 10, experiments were carried out toassess the 3-O-demethylation of NME with various demethylation reagents.The reactions were carried out at approximately 120° C. unless otherwisespecified and monitored by HPLC. The conditions were not optimized andserve to illustrate only that the reaction may be performed with thereagents listed.

Conversion (% area by Base Thiol HPLC) Sodium t-butoxide Methyl 3- 96.0%norbuprenorphine mercaptopropionate after 42 hours (at 150° C.) Sodiumt-butoxide Propanethiol 82.0% norbuprenorphine after 19.8 hoursPotassium t-butoxide Propanethiol 86.3% norbuprenorphine after 18.5hours

Example 12: Alternative Bases

Based on the procedure of Example 10, experiments were carried out toassess the 3-O-demethylation of NME with various bases. The reactionswere carried out at approximately 120° C. unless other specified andmonitored by HPLC. The conditions were not optimized and serve toillustrate only that the reaction may be performed with the reagentslisted.

Conversion (% area by Base Thiol HPLC) Sodium t-butoxide Propanethiol82.0% norbuprenorphine after 19.8 hours Sodium ethoxide Propanethiol59.36% norbuprenorphine after 20 hours Sodium hydroxide Propanethiol63.94% norbuprenorphine after 20 hours NaH 1-Dodecanethiol 87.05%norbuprenorphine after 10.5 hours n-BuLi 1-Dodecanethiol 45.88%norbuprenorphine after 9.5 hours NaNH₂ 1-Dodecanethiol 58.09%norbuprenorphine after 20 hours Triethylamine 1-Dodecanethiol 0.17%norbuprenorphine (comparative) after 4.5 hours

The results in the table above demonstrate that alkoxides (such assodium butoxide or ethoxide), hydrides, organolithium reagents (such asn-butyllithium) and amides (such as sodium amide) can be used in theprocesses of the present invention.

Triethylamine was also assessed but only a very low level of product wasdetected (0.17%). This is considered to be as a result of the similarityin pKa estimated for alkyl thiols and the conjugate acid oftriethylamine.

Example 13: Alternative Solvent

The procedure of Example 10 was repeated using N-methyl-2-pyrrolidone(NMP) as the solvent, sodium t-butoxide and propanethiol to givenorbuprenorphine (88.71% by area conversion by HPLC) after 18.5 hoursreaction time.

Example 14: 0-Demethylation of N-cyano-3-O-methyl-norbuprenorphine

Following the procedure of Example 10,N-cyano-3-O-methyl-norbuprenorphine was 3-O-demethylated toN-cyano-norbuprenorphine after two hours (77.57% area conversion). LCMSanalysis confirmed that the target product has formed. Nonorbuprenorphine was detected i.e. no cleavage of the cyano groupoccurred under the reaction conditions.

Example 15: Attempted O-demethylation of 3-O-methylbuprenorphine(Comparative)

Potassium tert-butoxide (1.75 g, 15.60 mmoles) was charged to a flaskround bottomed flask fitted with an overhead stirrer, condenser,temperature probe and nitrogen bubbler. The flask was purged withnitrogen. DMF (40 mL) was charged to the flask and the mixture wasstirred. A sharp solution was formed. 1-Dodecanethiol (3.7 mL, 15.56mmoles) was added and a thick, white precipitate was formed, which wasallowed to stir out for 30 minutes. 3-O-Methylbuprenorphine (5.00 g,10.38 mmoles) was added to the slurry and the reaction mixture heated to120° C. The reaction mixture was heated at this temperature for 3 hours15 minutes. After this time, the reaction mixture was analysed by HPLC.HPLC analysis indicated that 94.4% starting material remained and only2.1% buprenorphine had been produced.

The demethylation was then attempted using sodium propanethiolate todetermine if there were steric interactions preventing the long chainthiolate from participating in the demethylation reaction. However, thisreaction was also unsuccessful and no product was detected.

Example 16: Attempted O-Demethylation of Other Morphinans (Comparative)

Using the procedure as described in Example 10, the O-demethylations ofthebaine, hydrocodone and oxycodone were attempted:

Target Product Starting Material Target Product Sample Point (% area byHPLC)

 4 hours 21 hours 20.79%  1.63%

 4 hours 21 hours 2.35% 8.61%

 4 hours 21 hours 3.92% 0.49%

Although some oripavine was formed from thebaine, the reaction wasinefficient and an extended reaction time resulted in decomposition orfurther reaction of the product. As such, opiates containing the dienefunctionality do not appear to be stable to the demethylation reactionconditions.

Similar results were observed with hydrocodone or oxycodone as thestarting material where it appears that the ketone functionality is notstable to the demethylation reaction conditions.

Example 17: O-Demethylation of Protected Oxycodone

Oxycodone hydrochloride (30.0 g), ethylene glycol (60 mL, 12.6 eq) and acatalytic amount of para-toluenesulfonic acid (3.24 g, 0.2 eq) intoluene (1200 mL) were heated to reflux with the azeotropic removal ofwater. The reaction was heated over approx. 30 mins to 110° C. and aclear colourless solution was obtained. The reaction mixture was allowedto cool to room temperature and the pH adjusted from pH 6 to pH 9 with0.88 ammonia solution (7.6 mL). The product was extracted intochloroform, washed with brine and dried over sodium sulfate. The solventwas removed and the product treated with methanol. After removal of themethanol, the white powder was dried to give oxycodone ketal (27.91 g).

Potassium tert-butoxide (18.73 g, 3 eq) was charged to a flange flaskfitted with an overhead stirrer, condenser, temperature probe andnitrogen bubbler. The flask was purged with nitrogen. DMF (140 mL) wascharged to the flask and the mixture was stirred. 1-Dodecanethiol (40mL, 3 eq) was added and a thick, white precipitate was formedimmediately. Oxycodone ketal (20.0 g) was added to the slurry and washedin with 20 mL DMF. The reaction mixture was heated to 120° C. and washeated at this temperature for approximately 8.25 hours. After thistime, the reaction mixture was analysed by HPLC (λ=245 nm) and theresults showed oxymorphone ketal (70.28% area) and oxymorphone (24.28%area) has formed.

All of the patents, published patent applications, journal articles, andother references cited in the present disclosure are incorporated byreference herein in their entireties for all useful purposes.

What is claimed:
 1. A process for the preparation of a compound offormula (Ib),

wherein: R₁₀ is a straight-chain, branched or cyclic C₁-C₂₀ alkyl; R₁₁is C(R₁₃)(R₁₄)(OH) or a protected C(═O)(R₁₅); R₁₂ is H or CN; R₁₃ is astraight-chain, branched or cyclic C₁-C₂₀-alkyl; R₁₄ is astraight-chain, branched or cyclic C₁-C₂₀-alkyl; and R₁₅ is astraight-chain, branched or cyclic C₁-C₂₀-alkyl

is a double bond or a single bond; the process comprising: i. reacting acompound of formula (Ia) with a thiolate in a suitable polar aproticsolvent, wherein the thiolate is selected from the group consisting ofan optionally substituted C₁-C₂₀-alkylthiolate, an optionallysubstituted C₆-C₂₀-arylthiolate or an optionally substitutedC₇-C₃₀-arylalkylthiolate; and ii. treating the reaction mixture of step(i) with a protonating agent to give the compound of formula (Ib).
 2. Aprocess according to claim 1, wherein the thiolate is aC₁₀-C₂₀-alkylthiolate.
 3. A process according to claim 2, wherein theC₁₀-C₂₀-alkylthiolate is a dodecanethiolate salt.
 4. A process accordingto claim 1, wherein the thiolate is prepared from a thiol and a basewhich is capable of deprotonating the thiol.
 5. A process according toclaim 4, wherein the base is selected from the group consisting ofalkali metal alkoxides, alkali metal hydroxides, alkali metal hydrides,organolithium reagents and alkali metal amides.
 6. A process accordingto claim 1, wherein the polar aprotic solvent is selected from the groupconsisting of dimethylformamide, dimethylacetamide,N-methyl-2-pyrrolidone, dimethylsulfoxide, sulfolane,hexamethylphosphoramide and combinations thereof.
 7. A process accordingto claim 1, wherein the reaction of step (i) may be conducted at atemperature in the range of about 100° C. to about 130° C.